mirror of
https://github.com/bevyengine/bevy
synced 2024-12-30 06:53:13 +00:00
4847f7e3ad
Remove unnecessary calls to `iter()`/`iter_mut()`.
Mainly updates the use of queries in our code, docs, and examples.
```rust
// From
for _ in list.iter() {
for _ in list.iter_mut() {
// To
for _ in &list {
for _ in &mut list {
```
We already enable the pedantic lint [clippy::explicit_iter_loop](https://rust-lang.github.io/rust-clippy/stable/) inside of Bevy. However, this only warns for a few known types from the standard library.
## Note for reviewers
As you can see the additions and deletions are exactly equal.
Maybe give it a quick skim to check I didn't sneak in a crypto miner, but you don't have to torture yourself by reading every line.
I already experienced enough pain making this PR :)
Co-authored-by: devil-ira <justthecooldude@gmail.com>
116 lines
4.4 KiB
Rust
116 lines
4.4 KiB
Rust
use bevy_ecs::prelude::*;
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use rand::Rng;
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use std::ops::Deref;
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// In this example we will simulate a population of entities. In every tick we will:
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// 1. spawn a new entity with a certain possibility
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// 2. age all entities
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// 3. despawn entities with age > 2
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//
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// To demonstrate change detection, there are some console outputs based on changes in
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// the EntityCounter resource and updated Age components
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fn main() {
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// Create a new empty World to hold our Entities, Components and Resources
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let mut world = World::new();
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// Add the counter resource to remember how many entities where spawned
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world.insert_resource(EntityCounter { value: 0 });
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// Create a new Schedule, which defines an execution strategy for Systems
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let mut schedule = Schedule::default();
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// Create a Stage to add to our Schedule. Each Stage in a schedule runs all of its systems
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// before moving on to the next Stage
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let mut update = SystemStage::parallel();
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// Add systems to the Stage to execute our app logic
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// We can label our systems to force a specific run-order between some of them
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update.add_system(spawn_entities.label(SimulationSystem::Spawn));
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update.add_system(print_counter_when_changed.after(SimulationSystem::Spawn));
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update.add_system(age_all_entities.label(SimulationSystem::Age));
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update.add_system(remove_old_entities.after(SimulationSystem::Age));
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update.add_system(print_changed_entities.after(SimulationSystem::Age));
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// Add the Stage with our systems to the Schedule
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schedule.add_stage("update", update);
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// Simulate 10 frames in our world
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for iteration in 1..=10 {
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println!("Simulating frame {}/10", iteration);
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schedule.run(&mut world);
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}
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}
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// This struct will be used as a Resource keeping track of the total amount of spawned entities
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#[derive(Debug)]
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struct EntityCounter {
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pub value: i32,
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}
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// This struct represents a Component and holds the age in frames of the entity it gets assigned to
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#[derive(Component, Default, Debug)]
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struct Age {
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frames: i32,
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}
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// System labels to enforce a run order of our systems
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#[derive(SystemLabel, Debug, Clone, PartialEq, Eq, Hash)]
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enum SimulationSystem {
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Spawn,
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Age,
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}
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// This system randomly spawns a new entity in 60% of all frames
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// The entity will start with an age of 0 frames
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// If an entity gets spawned, we increase the counter in the EntityCounter resource
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fn spawn_entities(mut commands: Commands, mut entity_counter: ResMut<EntityCounter>) {
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if rand::thread_rng().gen_bool(0.6) {
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let entity_id = commands.spawn().insert(Age::default()).id();
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println!(" spawning {:?}", entity_id);
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entity_counter.value += 1;
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}
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}
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// This system prints out changes in our entity collection
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// For every entity that just got the Age component added we will print that it's the
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// entities first birthday. These entities where spawned in the previous frame.
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// For every entity with a changed Age component we will print the new value.
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// In this example the Age component is changed in every frame, so we don't actually
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// need the `Changed` here, but it is still used for the purpose of demonstration.
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fn print_changed_entities(
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entity_with_added_component: Query<Entity, Added<Age>>,
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entity_with_mutated_component: Query<(Entity, &Age), Changed<Age>>,
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) {
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for entity in &entity_with_added_component {
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println!(" {:?} has it's first birthday!", entity);
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}
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for (entity, value) in &entity_with_mutated_component {
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println!(" {:?} is now {:?} frames old", entity, value);
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}
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}
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// This system iterates over all entities and increases their age in every frame
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fn age_all_entities(mut entities: Query<&mut Age>) {
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for mut age in &mut entities {
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age.frames += 1;
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}
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}
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// This system iterates over all entities in every frame and despawns entities older than 2 frames
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fn remove_old_entities(mut commands: Commands, entities: Query<(Entity, &Age)>) {
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for (entity, age) in &entities {
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if age.frames > 2 {
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println!(" despawning {:?} due to age > 2", entity);
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commands.entity(entity).despawn();
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}
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}
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}
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// This system will print the new counter value everytime it was changed since
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// the last execution of the system.
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fn print_counter_when_changed(entity_counter: Res<EntityCounter>) {
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if entity_counter.is_changed() {
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println!(
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" total number of entities spawned: {}",
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entity_counter.deref().value
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);
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}
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}
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